Distributed Multi-writer Multi-reader Atomic Register with Optimistically Fast Read and Write

A distributed multi-writer multi-reader (MWMR) atomic register is an important primitive that enables a wide range of distributed algorithms. Hence, improving its performance can have large-scale consequences. Since the seminal work of ABD emulation in the message-passing networks [JACM '95], many researchers study fast implementations of atomic registers under various conditions. "Fast" means that a read or a write can be completed with 1 round-trip time (RTT), by contacting a simple majority. In this work, we explore an atomic register with optimal resilience and "optimistically fast" read and write operations. That is, both operations can be fast if there is no concurrent write. This paper has three contributions: (i) We present Gus, the emulation of an MWMR atomic register with optimal resilience and optimistically fast reads and writes when there are up to 5 nodes; (ii) We show that when there are > 5 nodes, it is impossible to emulate an MWMR atomic register with both properties; and (iii) We implement Gus in the framework of EPaxos and Gryff, and show that Gus provides lower tail latency than state-of-the-art systems such as EPaxos, Gryff, Giza, and Tempo under various workloads in the context of geo-replicated object storage systems

Stabilizing Server-Based Storage in Byzantine Asynchronous Message-Passing Systems

A stabilizing Byzantine single-writer single-reader (SWSR) regular register, which stabilizes after the first invoked write operation, is first presented. Then, new/old ordering inversions are eliminated by the use of a (bounded) sequence number for writes, obtaining a practically stabilizing SWSR atomic register. A practically stabilizing Byzantine single-writer multi-reader (SWMR) atomic register is then obtained by using several copies of SWSR atomic registers. Finally, bounded time-stamps, with a time-stamp per writer, together with SWMR atomic registers, are used to construct a practically stabilizing Byzantine multi-writer multi-reader (MWMR) atomic register. In a system of $n$ servers implementing an atomic register, and in addition to transient failures, the constructions tolerate t<n/8 Byzantine servers if communication is asynchronous, and t<n/3 Byzantine servers if it is synchronous. The noteworthy feature of the proposed algorithms is that (to our knowledge) these are the first that build an atomic read/write storage on top of asynchronous servers prone to transient failures, and where up to t of them can be Byzantine